The rare earth (or lanthanide) series of elements are those with atomic numbers 57 to 71 viz La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, respectively. Yttrium (Y, atomic number 39) is closely allied chemically. The rare earth elements are actually not as rare as implied by the name as cerium is more abundant than tin, yttrium more abundant than lead and all of the lanthanides are more plentiful than platinum group metals. The rare earth metal elements have a wide variety of uses, including as catalysts, in hardening alloys, glass additives, magnetic materials, phosphors, lasers, opthamalic lenses and optical fibers. Rare earth minerals are found in many forms, including oxides and multiple oxides, fluorides, carbonates and fluorocarbonates, silicates and phosphates.
Processes for the recovery of rare earth elements are known. Canadian Patent 1329486 of M. Matsua et al, issued 17 May 1994, discloses contacting a strongly acid solution of rare earth elements with a chelate resin having phosphorus-atom containing functional group. Canadian Patents 1217637 of P. Mein, issued 10 Feb. 1987, and 2015057 of K. S. Pisarcyzk at al, issued 27 Jul. 1999, describe digestion of pollucite with hydrochloric acid to obtain a solution of metal chlorides including cesium chloride. Canadian Patent 2021415 of G. D. Fulford et al, published 19 Jan. 1991, describes recovery of rare earth elements from sulphurous acid solution. Canadian Patent 1040756 of P. Broman at al, issued 17 Oct. 1978, describes use of flotation processes. Canadian Patent 2631190 of S. J. Mackowski et al, published 2 Nov. 2009, describes pre-leaching a composite ore of monazite and apatite minerals using an acid to substantially dissolve the apatite.
In other mining industries, processes have been developed to extract value metals e.g. nickel and titanium, with recycling of solutions used in the process and with substantially reduced environmental issues. One example is the use of solutions of hydrochloric acid and magnesium chloride in the extraction of titanium from titanium-bearing ores or concentrates at low temperatures, as disclosed in U.S. Pat. No. 7,803,336 of V. I. Lakshmanan, R. Sridhar et al, issued 28 Sep. 2010. U.S. Pat. No. 7,736,606 of V. I. Lakshmanan, R. Sridhar et al, issued 15 Jun. 2010, describes extraction of base metal sulphide ores with a lixiviant of a chloride, an oxidant and hydrochloric acid. The leaching may be conducted to limit the co-dissolution of platinum group metals and gold with the base metals.
Processes that are effective for the recovery of rare earth elements from rare earth element-bearing ores or concentrates and which have low or minimal environmental issues would be beneficial. Such processes should include potential for recycling of components used in the process so as to reduce environmental issues and for economic operation of the process. In addition, processes should be capable of separating rare earth elements from other value metals in leaching steps. There is a particular need for such processes in the rare earth element mining industry.